The present invention relates to spectroscopy systems and in particular to a high-speed spectroscopy system suitable for analyzing highly dynamic systems.
Spectroscopy studies the interaction between a material or materials and different frequencies of light to characterizes the spectral response of materials, such as gases, liquids, aerosols, solids, particulates, fiber-optic components etc. as may be related to physical properties of the material under test (e.g., temperature, pressure, velocity, composition, size, stress/strain. The interaction studied can be absorption, or reflectivity, scattering, fluorescence, etc.
The material being studied by spectroscopy may alternatively be a sensor constructed to modify particular light frequencies based on a measured parameter. One type of sensor is a fiber-Bragg grating (FBG) in which a fiber optic is treated to reflect a single frequency of light passing along its length. The reflected frequency is a function of a periodic variation in the fiber's index of refraction impressed on the length of the fiber. Physical changes in the fiber, such as caused by strain or thermal expansion, change the frequency of this reflected light allowing indirect measurements of temperature and strain.
High speed spectroscopy may be performed by applying a multispectral pulse to the material being studied then collecting the light modified by the material with a fiber optic which provides a variable delay in frequencies of the light pulse proportional to light frequencies. Spectroscopic analysis can then be performed by detecting the change in intensity of the light as a function of time and relating the time scale to frequency. Such a system is described in “Time of Flight Optical Spectrometry with Fiber Optic Wave Guides” by William Whitten published in Analytical Chemistry, Volume 54, Number 7, June 1982. In this device, a narrow band laser illuminates a chamber containing CCl4 to create the multispectral pulse, which is then used to illuminate a test cell.
The CCl4 chamber is cumbersome and causes a loss of coherence in the light signal from the laser. Coupling the light from the test cell to the fiber is difficult.